المعنى الاصطلاحي :

Remembering Allah (mentioning His name) by saying "lā ilāha illā 'llāh".

الشرح المختصر :

Saying "lā ilāha illā 'llāh" is the highest level of faith and the best Dhikr (remembrance of Allah) because it comprises the monotheism, which is the basis of faith. It is a word that distinguishes the dwellers of Paradise from the dwellers of Hell. It is a means of bliss for the dwellers of Paradise and one's Islam is not valid without it. Anyone whose final words are "lā ilāha illā Allāh" enters Paradise. With respect to "taḥmīd (saying "al-ḥamdu li 'llāh") and "tasbīh" (saying "subḥān Allāh); "tahlīl" is analogous with the root to the branches. That is to say, "tahlīl" is the root and any other form of Dhikr is a branch and is subsidiary. There are a number of forms of "tahlīl", which include: -"lā ilāha illā Allāh waḥda-hū lā sharīka la-h" (there is no true god but Allah alone, He has no partner); -"lā ilāha illā Allāh waḥdahū lā sharīka lah, la-hul-mulk wa la-hul-ḥamd wa-huwa `alā kulli shay'in qadīr" (there is no true god but Allah alone, He has no partner; to Him belongs sovereignty and to Him belongs praise and He is Powerful over all things); -"lā ilāha illā 'llāh waḥdahū lā sharīka lah, lahul-mulk wa lahu 'l-ḥamd, yuḥyī wa-yumīt wa-huwa `alā kulli shay'in qadīr" (there is no true god but Allah alone, He has no partner; to Him belongs sovereignty and to Him belongs praise, He gives life and death, and He is Powerful over all things). Specific dhikr (remembering) of Allah has to be with the authentic wording, while general dhikr does not necessitate it.

التعريف اللغوي المختصر :

"Tahlīl": raising the voice with something, raising the voice to inform about something.